As is known in the art, variable phase-shifter-attenuators have a wide range of applications. One such application is in phased array antennas where the direction and shape of the antenna beam is formed in accordance with the relative phases and attenuations produced across an array of antenna elements by variable phase-shifter-attenuators in the paths passing radio frequency energy between array of antenna elements and the radar system in accordance with control signals produced by a beam steering computer and fed to the phase-shifter-attenuators.
As is also known in the art, it would be desirable to provide digitally controlled variable phase-shifter-attenuators suitable for fabrication as a monolithic microwave integrated circuit (MMIC). One digitally controlled phase shifter is described in a paper entitled “A Wideband CMOS Linear Digital Phase Rotator”: by Hug Wang and Ali Hajimiri, IEEE 2007 Custom Integrated Circuit Conference, pages 671-674 (Vol. TP-30, pp. 1-4). In this paper, the phase rotator while proving phase rotation did not provide for variable attenuation. See also papers by K. Koh and G. Rebiez entitled “0.13 μm CMOS Phase Shifters for X-Ku- and K-Band Phased Arrays” IEEE Journal of Solid State Circuits. Vol. 42. No. 11 pp. 2535-2546 (2007) and S. Jeon, Y. Wang, H. Wang, F. Bohn, A Natarajan, A. Babakhani, and A. Hajimiri, “A Scalable 6-to-18 GHz Concurrent Dual-Band Quad-Beam Phased-Array Receiver in CMOS” IEEE Journal of Solid State Circuits, Vol. 43, No. 12. pp. 2660-2677 (2008).
As described in the paper “A Wideband CMOS Linear Digital Phase Rotator”: by Hug Wang and Ali Hajimiri, IEEE 2007 Custom Integrated Circuit Conference, pages 671-674, an input signal is separated into a pair of quadrature channels, each channel having n amplifiers of different gain. The input signal in each channel is fed to all n amplifiers. The on-off states of the amplifiers are controlled a digital control word. The outputs of the amplifiers in each of the channels are fed to a common output node. With such an arrangement, a plurality of 2(2n) phase shift-attenuation states is produced a Cartesian coordinate system having as the axis thereof the amplitudes of the output signal at one of the common nodes and the amplitudes of the output signal at the other one of the common nodes. The control word selects one of the 2(2n) states. The arctangent of the ratio of these two output signals at a selected one of the states is the phase provided to the input signal and the distance from the origin to the selected state is the attenuation provided to the control word.
In accordance with one embodiment, a phase shifter-attenuator system is provided having: a controller for producing a digital word representative of a predetermined phase shift and attenuation provided to an input signal; and a phase rotator for providing one of a plurality combinations of phase shift-attenuation states to the input signal selectively in accordance with one portion of the produced digital word, the plurality of combinations being distributed over a selected range of attenuations, the range being selected in accordance with a second portion of the produced digital word.
In one embodiment, a phase shifter attenuator system, comprises: (A) a controller for producing a digital word representative of a predetermined phase shift and attenuation provided to an input signal; and (B) a phase shifter-attenuation section. The a phase shifter-attenuation section comprises: (a) a phase rotator for providing one of a plurality combinations of phase shift-attenuation states to the input signal selectively in accordance with one portion of the produced digital word; and (b) an attenuation section for distributing the plurality of combinations of phase shift-attenuation states over a selected range of attenuations, such range being selected in accordance with a second portion of the produced digital word.
In one embodiment, the attenuator is a switchable bias circuit for switching an operating point of the phase rotator and in another embodiment the attenuator is a switchable attenuator fed by the phase rotator.
With such an arrangement, while the shifter-attenuator section produces of one of a 2(2n) discrete phase shift-attenuation states selectively in response to an 2n bit digital control word, the 2(2n) discrete phase shifts are distributed over a selected attenuation range selected in accordance with a second m bit portion of the digital word; such second portion being representative of 2m different ranges. Thus, the 2(2n) states may be distributed, for example where m is 1, over a large range of attenuations where a smaller amount of attenuation is selected or over a smaller range of attenuations where a higher degree of attenuation is desired. Thus, a greater number of states are available when larger attenuations are selected than the number of states available when smaller attenuations are selected. To put it another way, phase shifter-attenuator section operates over different selectable dynamic ranges, each range being associated a selected range of attenuations, and the 2(2n) discrete phase shift-attenuation states are distributed over each selected dynamic range so that each selected attenuation range has the full 2(2n) discrete phase shift-attenuation states.
In one embodiment, a phase shifter-attenuator system is provided having: (A) a quadrature section for converting an input signal into a corresponding pair of quadrature signals with each one pair of quadrature signals having an in-phase component and an out-of-phase component; (B) a controller for producing a digital word representative of a predetermined phase shift and attenuation provided to the input signal; (C) a phase shifter-attenuator section fed by the produced digital word, comprising: (a) a pair of quadrature channels, each one of the channels being fed a corresponding one of the pair of quadrature signals, each one of such channels having: (i) a plurality of amplifiers, each one the amplifiers having a different gain, each one of the amplifiers being fed by the corresponding one of the pair of quadrature signals fed to such one of the channels, the amplifiers in such one of the channels being coupled to an output node; (D) wherein the phase shifter-attenuator section provides one of a plurality combinations of phase shift-attenuation states to the input signal selectively in accordance with one portion of the produced digital word, the combinations being distributed over a selected range from the origin of a four quadrants of a attenuation-phase array, the range being selected in accordance with a second portion of the digital word.
In one embodiment, a phase shifter-attenuator system is provided, comprising: (A) a quadrature section for converting an input signal into a corresponding pair of quadrature signals with each one pair of quadrature signals having an in-phase component and an out-of-phase component; (B) a controller for producing two pairs of n bit digital words and a pair of m bit digital word, where n and m are integers, one of the pairs of n bit digital words being a first word WI having n bits and the complement of the first digital word, WI having n bits, and the other one of the two pairs of n bit digital words being a second word WQ having n bits, and the complement of the second word, WQ, having n bits, such 2n+m bit digital words being representative of a predetermined phase shift and attenuation provided to the input signal; (C) a phase shifter-attenuator section fed by the two pairs of n bit digital words and a pair of m bit digital word, comprising: (a) a pair of quadrature channels, each one of the channels being fed a corresponding one of the pair of quadrature signals, each one of such channels having: (i) a plurality of n amplifiers, each one the amplifiers having a different gain, each one of the amplifiers being fed by the corresponding one of the pair of quadrature signals fed to such one of the channels, each one of amplifiers in such one of the channels being coupled to an output node, and each one of the amplifiers being fed one of the n bits of the first digital word of one of the two pairs of digital words and n bits of the second digital word of said one of the two pairs of digital words; (D) wherein the phase shifter-attenuator section provide, in response to the two pairs of digital words fed thereto, a one of 2m*2(2n) combinations of phase shift-attenuation states to the input signal over a selected one of a plurality of ranges of attenuations, such one of the combinations being selected in accordance with the 2n bit digital word, such one of the ranges being selected in accordance with the m bit digital word.
With such embodiment, a large range of variable gain/attenuation is achieved without losing phase accuracy. This combines the phase rotator with a coarse attenuator used externally, or by coarsely changing the gain of all states by modifying the current supplied to the circuit digitally. When these external methods are used to provide large (˜10 dB) changes in attenuation, the fine control of the phase rotator is used to provide desired amplitude states at higher amplitude resolution within coarsely-tuned attenuation states.
The combination of a coarsely-tuned attenuator (or, in one embodiment, bias controller) to the intrinsic fine amplitude control of the phase rotator enables high phase resolution to be maintained over a wide range of attenuator values. Previous methods either fail to achieve a wide amplitude tuning range, or fail to maintain phase resolution as attenuation is increased. Two possible methods to achieve this function are described and include a combination of course and fine attenuation control, such that high phase resolution can be maintained over a wide tunable range of attenuator settings.
The details of one or more embodiments of the disclosure are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the disclosure will be apparent from the description and drawings, and from the claims.
Like reference symbols in the various drawings indicate like elements.